Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$112.98	12.239%	$126.8076	$126.81	$126.80	$126.80
Purchase #2	$109.55	7.212%	$117.4507	$117.45	$117.45	$117.50
Purchase #3	$66.29	13.739%	$75.3976	$75.40	$75.40	$75.40
Purchase #4	$27.85	3.533%	$28.8339	$28.83	$28.85	$28.80
Purchase #5	$40.83	6.485%	$43.4778	$43.48	$43.50	$43.50
Purchase #6	$111.89	10.368%	$123.4908	$123.49	$123.50	$123.50
Purchase #7	$135.26	11.172%	$150.3712	$150.37	$150.35	$150.40
7 purchase totals =	$604.65		$665.8296	$665.83	$665.85	$665.90